behavioral plasticity CH8: development of learning in songbirds behavioral analysis of birdsong singing in the brain

PART 4: BEHAVIORAL PLASTICITY #17: DEVELOPMENT OF LEARNING IN SONGBIRDS II • behavioral plasticity • CH8: development of learning in songbirds • behavioral analysis of birdsong • singing in the brain • summary

ANATOMY • song structures... 2 pathways • song production pathway  • anterior forebrain pathway ... not directly related to song production • found only in birds that • learn to sing • use feedback

ANATOMY • song structures... 2 pathways • song production pathway  • higher vocal center • robust nucleus of the archistriatum • tracheosyringeal portion of the hypoglossal nucleus  syringeal musculature • anterior forebrain pathway 

ANATOMY • song structures... 2 pathways • song production pathway  • anterior forebrain pathway  • area X • medial portion of the dorsolat. thalamus • lateral portion of the magnocellular nucleus of the anterior neostriatum

ANATOMY • pathways interconnected at several points • oversimplified here (!)... most studied illustrated only • other bits and connections not discussed... eg

LATERALITY • some functions carried out primarily / exclusively by 1 side of the brain... laterality... many familiar egs • syrinx innervated by L & R hypoglossal nerve XII

LATERALITY • some functions carried out primarily / exclusively by 1 side of the brain... laterality... many familiar egs • syrinx innervated by L & R hypoglossal nerve XII • transect R side • modest effect • transect L side • severe effect • hypoglossal dominance

LATERALITY • interesting observations... some spp. of birds are hypoglossal dominant... • left (chaffinch, canaries) • right (zebra finches) • neither

LATERALITY • laterality in other systems higher in the brain... • lesions in brain...HVc in adult canaries... • R lesions mile • L lesions severe • hemispheric dominance

LATERALITY • permanent effect of HVc lesions in canaries ? • can gradually relearn song • lesions overcome by HVc in R hemisphere • subsequent lesion in R HVc • removes song permanently • cellular mechanisms not well understood known

SEASONAL VARIATION & NEUROGENESIS • neural changes in identified structures / seasons ? • in adults... in spring (vs fall) sizes of • HVc 99% increased • RA 76% increased • ~ increased song repertoire

SEASONAL VARIATION & NEUROGENESIS • HVc & RA • ~ increased song repertoire in s & s • in s (non-singers) < s • increase in s + testosterone

SEASONAL VARIATION & NEUROGENESIS • how to increase brain size ? • new neurons... neurogenesis • new projections • new synapses... synaptogenesis • all of the above ? • important questions about “adult” nervous systems: • are new neurons born ? • do they connect properly ? • do they function properly ?

SEASONAL VARIATION & NEUROGENESIS • some birds show • seasonal variation in anatomy & song • no seasonal variation in anatomy but do have seasonal changes in song... • HVc size increase accompanied by neurogenesis • intriguing hypothesis: replacement of old neurons with new ones as birds replace old songs with new ?

SEASONAL VARIATION & NEUROGENESIS • neurogenesis in songbirds • 20 – 65 days post-hatching • new neurons added to HVc & area X • occurs ins > s (non-singers) • 50% project from HVc  RA • ~ song learning sensitive phase • sexual dimorphism

SEASONAL VARIATION & NEUROGENESIS • new neurons during sensory or sensorimotor phase ? • can’t address in zebra finch, phases overlap • in white-crowned sparrow... • change during peak of sensory acquisition phase • little change in sensory motor phase •  in swamp sparrow, neurogenesis  song learning

ANTERIOR FOREBRAIN PATHWAY • not important for normal song production... but • important for sensory learning & auditory matching • juvenile zebra finches... lesions in LMAN disrupts •  subsequent learning of song • not needed for song maintenance • similar results found for area X & DLM

ANTERIOR FOREBRAIN PATHWAY • what kinds of information processed by pathway ? • lesions in zebra finches • LMAN  monotonous repetition, 1-note clusters, arrests further song plasticity (premature stabilization) • area X  rambling & long • authors suggest LMAN  • sends feedback  area X • maintain plasticity in RA • site of steroid hormone activity

CELLULAR ANALYSIS • song production • in HVc & RA... premotor areas • neuron activation before, during, after song • activity in HVc precedes RA • HVc for whole song • RA for syllables

CELLULAR ANALYSIS • song production • in HVc & RA... premotor areas • stimulate HVc during singing, • phase advance of song • ~ reset of pattern • not ~ feedback • HVc neurons ~ song pattern generator • RA neurons receive signal, do not generate pattern

CELLULAR ANALYSIS • auditory selectivity • song feedback critical • response sites ? • anterior forebrain pathway

CELLULAR ANALYSIS • auditory selectivity • song feedback critical • response sites ? • anterior forebrain pathway • own song  • reversed  • conspecific 

CELLULAR ANALYSIS • auditory selectivity • song feedback critical • response sites ? • anterior forebrain pathway • own song  • reversed  • conspecific  • LMAN > area X... hierarchy • successive sites  greater selectivity

CELLULAR ANALYSIS • auditory selectivity • HVc RA (song production pathway) area X (anterior forebrain pathway) • projections from 2 distinct HVc cell populations • all 3 structures “selective”

CELLULAR ANALYSIS • auditory selectivity • caudal medial neostriatum (NCM) • gene transcription regulated by conspecific song • immediate-early gene activation... zenk • rapid activation • response to signals • only on first exposure... involved in learning

compared CELLULAR ANALYSIS • differential developmental timetables in song system • 2 pathways from HVc develop at different times 1. indirect HVc  ...  RA @ 2 weeks posthatch • ~ learning • template 1st 2. direct HVc  RA @ 3-4 weeks posthatch • ~ singing • own song 2nd

CELLULAR ANALYSIS • differential developmental timetables in song system • 2 pathways from HVc develop at different times 1. indirect HVc  ...  RA @ 2 weeks posthatch 2. direct HVc  RA @ 3-4 weeks posthatch • correlated innervation • different transmitters & receptors • different types of synapses  RA • convergence at RA ?

CELLULAR ANALYSIS • differential developmental timetables in song system • when are HVc neurons song-selective ? • white crown sparrows • not until after gap... during sensorimotor phase • not for tutoring (sensory) but for listening to self

CELLULAR ANALYSIS • sexual dimorphism in the bird brain • all song nuclei > • HVc volume ~ song complexity • : ~ song

CELLULAR ANALYSIS • sexual dimorphism in the bird brain • why do non-singings have song nuclei ? • some do sing in response to  song • lesion in HVc removes discriminative ability • important for song perception in s • same circuitry used differently by s &s

SUMMARY • bird song simple  complex • acoustic architecture: notes, syllables, phrases • species typical song + dialects • phases of song development • sensory: learning by example from others • sensory motor: subsong, plastic song • crystallized song: stable song • some spp. have overlap, some have separation

SUMMARY • auditory feedback critical for sensorimotor acquisition • song template = innate + learned components • song usually sexually dimorphic • steroid hormones  development, seasonal expression of song, song learning • 2 interacting & converging brain circuits (at RA): • song production pathway • anterior forebrain pathway

SUMMARY • auditory neurons selective for own song • sites for processing auditory feedback • sequential activation of HVc  RA premotor neurons • part of song pattern generator in HVc • anatomical sexual dimorphism ~ song generation • song nuclei important for song perception in s

behavioral plasticity CH8: development of learning in songbirds behavioral analysis of birdsong singing in the brain